The present invention generally relates to loudspeaker horns, and more particularly to the problem of designing a loudspeaker horn having uniform horizontal and vertical polar frequency responses.
One of the main problems associated with loudspeaker horns is the difficulty of designing the horn to provide uniform horizontal and vertical polar frequency responses over the horn's operating frequencies. This difficulty leads to "beaming" and high frequency on-axis drop-out associated with horn loaded loudspeakers. In other words, the horn may behave in a desired fashion and provide desired coverage at certain frequencies but degrade markedly at other frequencies, resulting in a poor overall performance. These performance problems can be traced to the failure of conventional designs to provide the phase correction necessary at the mouth of the horn to achieve a desired uniform frequency response. They exist in a variety of horn designs including exponential horns, multicell horns and sectional horns.
In pure exponential horns, the driver mechanism of the speaker couples to a narrow unobstructed throat area of the horn which is typically small in relation to the wavelength of the frequencies at which the speaker operates such that no phase correction is possible at the mouth end of the horn. Multicell and sectional horns provide a variety of vane and cell structures intended to improve the directivity and some improvement to phase control, but the introduction of vanes or cellular structures into the throat area of the horn tends to introduce undesirable ripples in the frequency response. U.S. Pat. Nos. 4,390,078 to Howze et. al. and 4,685,532 to Gunness disclose examples of rectangular horns employing one or more vanes intended to provide constant coverage angles and eliminate interference related to high frequency drop-out, but for reason mentioned above generally produce unsatisfactory results in terms of frequency response uniformity.
Yet another problem associated with some conventional horn designs is illustrated in U.S. Pat. No. 4,187,926 to Henricksen et. al. Henricksen discloses a horn having an elongated throat area having a short dimension relative to the wavelengths of the high frequencies at which the horn operates. This length will introduce distortion to the sound wave as it passes through the throat area. Generally, the throats found in many early horn designs have lengths that are many times the wavelength of their high operating frequencies with the serious distortive effect.
The present invention provides an loudspeaker horn structure and a method for coupling sound pressure waves from an acoustical driver into free space which achieves substantial uniformity in the horn's frequency response and which substantially reduces the problem of beaming and high-frequency drop-out associated with conventional horn designs. The loudspeaker horn of the present invention also provides a horn design which has a relatively short dimensions at the throat end of the horn, resulting in reduced distortion after introduced into this section of the horn.